Are we witnessing the evolution of money?

If you've looked closely at a £20 banknote lately, you may have noticed something strange. In small letters, just below the words “Bank of England” it will say: “ I promise to pay the bearer on demand the sum of twenty pounds .” What does that really mean? If you think about it, that doesn't make much sense. When you pay someone £20 in cash, the note itself is the payment - it's not an IOU note. If you go to a bank and ask them to fulfill that promise, they'll simply give you...